1. Field of the Invention
The present invention relates to an electric power supply system cooperated by a battery and a super capacitor and, more particularly, to an electric power supply system capable of avoiding excessive charging and excessive discharging of a battery.
2. Description of the Related Art
Due to environmental awareness, power sources using electricity are utilized in multiple applications, such as electric vehicles (EV), battery electric vehicles (BEV), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), or energy storage systems (ESS), are prosperous.
In order to achieve a better cruising endurance of the above electric vehicles, a large-capacity battery, such as a battery unit consists of a plurality of LiFePO4 batteries, is generally required to serve as the core power source module of the above electric vehicles to meet the power supply demand for the actual vehicle load.
Although a LiFePO4 battery has a high energy density, an excessively large current is extracted or released from the battery at the moment of acceleration or deceleration. If the electricity is only supplied by the LiFePO4 battery, dramatic reaction of chemical substances in the LiFePO4 battery could occur and result in an increase of the working temperature, leading to adverse effects to the performance and the service life of the battery. Although improvement has been made by scholars, such as “A Parallel Power Supply System by LiFePO4 Battery and Super Capacitors” published by Yue-wei Huang in The 17th National Conference on Vehicle Engineering, this conventional technique requires three circuits (including a voltage increasing/decreasing circuit and two voltage decreasing circuits) for transporting the electric energy, increasing the size of the circuits and the costs.
Thus, a need exists for solving the disadvantages of the conventional techniques to avoid excessive charging or discharging of the battery, increasing the battery performance and prolonging the service life of the battery for the purposes of meeting the actual demand and increasing the utility.